APU overheating causing reboots

So I recently RMA'd my main hardware and decided to run my old A8-3850 rig in the mean time. Issue is there are extremely annoying reboots after core temp reaches 75'ish area. Thing is I lowered to core ration is 16x and the issue still persists. I'd be willing to disable cores if I could but the motherboard doesn't support that.MSI A55M-P33 using stock cooler, reapplied thermal paste twice it's not the issue and the case is an ATX case with rear 120mm exhaust so there's more than enough airflow.

By default the fans are set to run at 100% which is quite annoying. I just want the PC to be reasonably quiet so I enable the smart fan control which ramps up at 70 degrees'ish but the CPU temp still climbs and ultimately turns off.

I just want to browse the web basically, not looking to game or anything so if anyone knows how to further limit the CPU so I can at least use the PC it'd be great if you told me.

Operates nicely at 35 degrees when everything is dormant but the moment you load a webpage or open a program it climbs quickly to 75 degree range. I have an AIO water cooler from the rig I RMA'd I'd really not like to install it just to browse the web on this machine

Just realized there's no way this could be the CPU's temp because it often drops to 10 degrees C which is way below ambient room temp. I'm using Core Temp. Not familiar with AMD brand so I just went for my go-to in terms of temp monitoring for processors.

Thanks for the reply. Also thanks for bringing it to my attention. I've been using the Control Center tool that came with the motherboard and it seems to be alot more accurate. Higher temps are similar to that of Core Temp just generaly 5-10 degrees lower but the low end CPU temp is actually proper in terms of what you can expect from a CPU with a stock cooler during idle i.e 35-40 degrees.